This invention relates to a vehicle differential having multiple modes of operation and more particularly to a shift mechanism for shifting the differential between the different modes.
A substantial number of vehicles are designed to have the versatility of two-wheel drive and four-wheel drive. In two-wheel drive, either the front pair of wheels or the rear pair of wheels are connected to the vehicle""s power source. In four-wheel drive, both the front and rear pair of wheels are connected to the power source.
Each pair of wheels have a pair of axles connected to a differential which in turn is connected to a propeller shaft driven by the vehicle""s power source. A front propeller shaft is connected to the front differential and a rear propeller shaft is connected to the rear differential. One of the propeller shafts is disconnected from the vehicle""s power source for two-wheel drive.
Referring to the differential for the wheel set that can be connected and disconnected from the power source (commonly the front wheel set or front pair of wheels), the primary function of the differential is to permit the left and right wheels to rotate at different speeds. This is accomplished by a gear assembly that includes a differential case that is rotatably driven by the propeller shaft. Opposing side gears in the differential case are coupled to the axles and the opposing side gears are coupled together by pinion or spider gears commonly referred to as differential gears which are rotatably mounted to the case of the differential.
The arrangement of gears in the differential transmits torque from the propeller shaft to the axles which in turn transmits the torque to a pair of front end or rear end wheels. The torque of the axles is always equal regardless of the speed of the axles relative to each other. When the axles are connected to wheels having similar tractive capacity, the axles rotate equally or, if the vehicle is in a turn, they rotate differently according to the turning radius of each wheel. Differential axle rotation in this case is desirable for normal vehicle operation. When the axles are connected to wheels having substantially different tractive capacity, the wheel having lesser tractive capacity may slip, thus causing the axle connected to it to turn faster than the axle connected to the wheel having greater tractive capacity. Differential axle rotation in this case is undesirable for normal vehicle operation.
The above explanation explains two circumstances or modes for a differential, i.e., allowing the differential to provide differential axle rotation and preventing differential axle rotation. A third desired mode occurs when the propeller shaft for that set of wheels is disconnected from the vehicle""s power source, i.e., the vehicle is placed in two-wheel drive. Once the propeller shaft is disconnected from the power source, the propeller shaft is passive (it does not convey a driving torque). However, it is still driven in that the wheels of that wheel set are forced to turn as the vehicle is driven in two-wheel drive and they drive the axles which drive the differential gears which drive the propeller shaft. In this event, it is desirable to separate or disconnect the propeller shaft from the driven axles (the third mode) to avoid unnecessary rotation of the propeller shaft and thereby save energy and wearing.
Accordingly, it is an object of the present invention to provide a shift mechanism for the differential for shifting the differential between the above-explained three modes.
In a preferred embodiment of the present invention, the propeller shaft is connected to a pinion gear that drives a ring gear that is connected to a differential case. The differential case (through a cross pin and spider gears) rotates opposing side gears, one of which rotates a first wheel axle and the other a stub axle. The stub axle is adjacent a second wheel axle and a clutch ring is movable between a position of engagement with only the stub axle or a position of engagement with both the stub axle and second wheel axle.
If the stub axle is locked to the second wheel axle, the wheels are driven as is typical for a differential as explained above. If the stub axle is unlocked from the second wheel axle, the stub axle rotates freely, i.e., with very little resistance in either direction of rotation. In such case, the propeller shaft is effectively uncoupled from the wheel axles. The first wheel axle, which is connected to the differential assembly will simply drive the differential gears and stub axle (and not the differential case) and thereby allow the propeller shaft and the ring gear and pinion gears to remain idle, assuming that the propeller shaft is also disconnected from the power source.
The clutch ring has a third position of engagement whereby it not only locks the stub axle to the second wheel axle but it locks both to the differential case. If either one of the wheel axles are locked to the case, the gears of the case are locked together and prevent relative rotation. Thus, both wheel axles are locked to the differential case and differential rotation of the wheels is prevented.
The structure for achieving this three mode positioning includes a clutch ring with inner and outer teeth. The stub axle and second wheel axle are in close adjacency and have matching outer splines. The inner teeth of the clutch ring produce engagement as between the stub axle and the second wheel axle. The differential case is configured to have a ring-shaped or flange portion with inner splines in close proximity to the juncture of the stub axle and second wheel axle. These inner splines of the case are matched to the outer splines of the clutch ring for engagement therebetween. In the desired arrangement, the clutch ring can be moved first into engagement with both axle portions and then, as desired, into engagement also with the inner splines of the differential case.
An actuator for actuating movement of the clutch ring includes an inner shift spring assembly connected to posts that extend axially through the differential case to position outside the case and connect to an outer shift ring. The shift ring, shift ring assembly and shift posts rotate with the case but have limited axial movement relative to the case. A shift shaft is coupled to the outer shift ring outside the differential case. The clutch ring is coupled to the inner shift spring assembly and posts at a position inside the differential case.
The shift shaft protrudes through the differential carrier where a power source produces the desired linear shifting movement of the shift shaft. The shift shaft does not rotate with the shift ring and thus the coupling to the outer shift ring includes a shift fork including bearing members that allow relative rotation as between the outer shift ring and shift fork but not axial/linear movement. This linear movement of the shift shaft produces linear movement of the shift fork and thus linear movement of the outer shift ring and posts. The clutch ring is rotatably fixed to the stub axle and in two of the three modes has to be capable of rotative motion relative to the differential case and thus the outer shift ring and posts. Thus, the coupling as between the posts and clutch ring includes bearing members (provided by the shift spring assembly) that allows relative rotation as between the posts/shift ring. Thus, linear movement of the shift rings (induced by the shift shaft) induces similar linear movement of the clutch ring.
The clutch ring movement is not always subject to instant selective movement and thus the coupling between the posts/shift ring and clutch ring is accomplished by compliant members of the spring assembly which urge the clutch ring into engagement. In the event the splines of the components to be engaged are not in alignment, the clutch ring is thus spring loaded toward engagement and achieves engagement when the splines become aligned. It can also happen that the splines become torque locked when disengagement is attempted and the compliant springs will similarly become spring locked until torque lock up is released.
The features as described above will be more fully understood and appreciated upon reference to the following detailed description and the accompanying drawings referred to therein.